Sheet delivery apparatus for printing presses including double stacker

ABSTRACT

The sheet delivery apparatus includes means for delivering sheets on a delivery conveyor either all to a selected one of two sheet stack receiving means, or alternate sheets to each stack receiving means. As another alternative, counted batches of sheets may be delivered alternately to the two sheet stack receiving means. A third sheet receiving means, of limited capacity is provided to receive selected sheets for inspection, and at times to receive other sheets. The sheet delivery chain carries sheet grippers and cam followers for operating the grippers to sheet releasing positions. The cam followers on alternate sheet grippers along the chain are spaced at one of two different locations laterally of the chain. Each sheet stack receiving means is provided with two retractable cams, spaced laterally corresponding to the two lateral locations of the followers. When any cam is moved from its retracted position to an active tripping position, it engages the cam followers on alternate grippers along the chain, so that alternate sheets are dropped from the chain at that location. Each sheet receiving means includes a stacker comprising two vertically extending opposed conveyors, each having retractable brackets projecting toward the opposite conveyor. Plates or pallets may be inserted on the brackets to receive the sheets. The conveyors are driven downwardly as the stack builds up. The brackets are retracted upon engagement with the edges of the stacked plates, so that the movement of the conveyors may continue after the motion of the plates is stopped.

'22 Filed:

United States Patent [191 D Amat0 et al.

[75] Inventors: Salvatore F. DAmato, Floral Park;

Chauncey P. Foote, Jr., Katonah, both of NY.

[73] Assignee: American Bank Note Company,

New York, NY.

June 21, 1973 [21] Appl. No.: 372,066

[52] U.S. C1. 271/64; 101/232; 271/183; 271/204; 271/218 [51] Int. Cl. B65I-I 29/04 [58] Field of Search 271/64, 204-206, 271/217, 218,183, 57; 214/6 H; 101/232 [56] References Cited UNITED STATES PATENTS 1,607,143 11/1926 White 271/64 X 2,010,732 8/1935 Mandusic 271/218 2,024,140 12/1935 Belluche.... 101/408 X 2,234,116 3/1941 Grupe 271/218 2,318,451 5/1943 Belluche et a1... 271/64 2,474,997 7/1949 Wormser 271/183 2,815,949 12/1957 Faeber 271/64 3,007,696 1l/l961 Wheeler et al. 271/56 3,366,253 1/1968 Walchhuter 214/6 H 3,672,265 6/1972 Schwarzkopf.... 271/204 3,759,177 9/1973 Gazzola et al. 101/408 X FOREIGN PATENTS OR APPLICATIONS 1,112,536 8/1961 Germany 271/204 [451 Sept. 23, 1975 Primary Exarrtiner-Evon C. Blunk Assistant Examiner-Bruce H. Stoner, Jr.

Attorney, Agent, or Firm-Cooper, Dunham, Clark, Griffin & Moran [57] ABSTRACT The sheet delivery apparatus includes means for delivering sheets on a delivery conveyor either all to a selected one of two sheet stack receiving means, or alternate sheets to each stack receiving means. As another alternative', counted batches of sheets may be delivered alternately to the two sheet stack receiving means. A third sheet receiving means, of limited capacity is provided to receive selected sheets for inspection, and at times to receive other sheets. The sheet delivery chain carries sheet. grippers and cam followers for operating the grippers to sheet releasing positions. The cam followers on alternate sheet grippers along the chain are spaced at one of two different locations laterally of the chain. Each sheet stack receiving means is provided with two retractable cams, spaced laterally corresponding to the two lateral locations of the followers. When any cam is moved from its retracted position to an active tripping position, it engages the cam followers on alternate grippers along the chain, so that alternate sheets are dropped from the chain at that location. Each sheet receiving means includes a stacker-comprising two vertically extending opposed conveyors, each having retractable brackets projecting to'watd the opposite conveyor. Plates or pallets may be inserted on the brackets to receive the sheets. The conveyors are driven downwardly as the stack builds 'up. The brackets are retracted upon engagement with'the edges of the stacked plates, so that the movement of the conveyors may continue after the motion of'th'e plates is stopped.

12 Claims, 18 Drawing Figures US Patent Sept. 23,1975 Sheet 1 of 15 3,907,274

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o {yr a m i g in .W Q NQN US Patent SHEET DELIVERY APPARATUS FOR PRINTING PRESSES INCLUDING DOUBLE STACKER CROSS-REFERENCES U.S. Pat. application, Ser. No. 173,555, filed Aug. 20, 1971, by lvaldo Gazzola et al., entitled Plate Wiping Mechanism for Intaglio Press, now U.S. Pat. No. 3,762,319, issued Oct. 2, 1973 discloses an apparatus which may be used on the same press with the present invention.

U.S. Pat. Application, Ser. No. 195,364, filed Nov. 3, 1971, by lvaldo Gazzola et al., entitled Apparatus for Delivering Sheets Onto a Moving Strip of Material", now U.S. Pat. No. 3,749,330, issued July 31, 1973 discloses another apparatus which may be used on the same press with the present invention.

U.S. Pat. Application, Ser. No. 298,443, filed Oct. 17, 1972, by lvaldo Gazzola et al., entitled Printing Pressure Control Apparatus for lntaglio Press, discloses another apparatus which may be used on the same press with the present invention.

U.S. Pat. Application, Ser. No. 298,444, filed Oct. 17, 1972, by lvaldo Gazzola et al., entitled Paper Feed Mechanism for Cylinder Press, now U.S. Pat. No. 3,828,673, issued Aug. 13, 1974 discloses another apparatus which may beused on the same press as the preset invention.

U.S. Pat. Application, Ser. No. 298,376, filed Oct. 17, 1972, by lvaldo Gazzola et al., entitled Apparatus for Fitting Flexible Printing Plates and Rigging to Printing Press Cylinders, now Patent No. 3,828,672, issued August 13, 1974 discloses another apparatus which may be used on the same press as the present invention.

U.S. Pat. Application, Ser. No. 302,126, filed Oct. 30, 1972, by lvaldo Gazzola et al., now Patent No. 3,822,644, issued July 9, 1974 entitled Apparatus for Maintaining Registry Between the Plates of a Multiple Plate Cylinder Press and Sheets Supplied Thereto, discloses another apparatus which may be used on the same press as the present invention.

BRIEF SUMMARY OF THE INVENTION The sheet delivery apparatus includes a delivery conveyor having a plurality of gripper means spaced along the conveyor, each gripper means being connected to a cam follower. Each gripper means is biased to a sheet gripping position and is shiftable to a sheet releasing position by its cam follower, which may be actuated to release its gripper means by a cam located along the path of the conveyor. The cam followers for two sets of alternate gripper means along the length of the conveyor are spaced at two different distances from the lateral edges of the conveyor. Two principal sheet stack receiving means are provided, where the delivered sheets can build up into stacks. A third auxiliary sheet receiving means has a limited capacity.

At each sheet receiving location there are two cams, each selectively movable between a retracted position and an active position in which it engages the cam folnected to crank arms on the respective sleeves for rotating the sleeves. The cylinders may be independently controlled, so that the cams may be set to release all sheets from the conveyor at any of three sheet receiving locations, or they may be set to release alternate sheets at one station, and the intervening sheets at the other station. Alternatively, all of the cams may be retracted so as to allow one or more sheets, as desired, to pass both of the stacking stations and go on to the third auxiliary sheet receiving location, sometimes referred to as the inspection station.

. A stacker at each of the two stack receiving means comprises two horizontally spaced, downwardly traveling opposed vertical conveyor means. The sheets are delivered between these two conveyor means in a substantially horizontal orientation. Each conveyor means includes retractable brackets projecting toward brackets at the same levels on the opposite conveyor means. The two conveyors means are synchronously driven, so that the brackets remain at the same levels. A plurality of plates or pallets may be provided, each of which is insertable in the stacker so as to be supported on a set of opposed brackets. Each plate is adapted to receive a section of the stacked sheets. A bottom support for the stack is inserted between the two vertical conveyor means at the bottom thereof. Typically, this bottom support will be a pallet adapted for removal by a fork lift truck or the like.

Each stacker may be operated selectively in either of two modes. In one mode of operation, only a single pallet is used. The pallet is inserted at the bottom of the vertical conveyors, and is wide enough so that its marginal edges are supported by the brackets. The conveyors are driven to lift the pallet to its uppermost position. The stack builds up on the pallet, which is moved downwardly as the stack builds up. When the pallet reaches the bottom of the conveyor, the pallet is removed, carrying the stack supported by it.

In the other mode of operation, the stack is separated periodically into sections by the insertion of plates or pallets, which rest on the brackets on the conveyor. The pallet at the bottom of the stack may or may not rest on the brackets. The height of each section plus its supporting plate is less than the spacing between brackets. During the building up of the stack, the greatest weight to which any sheet can be subjected is the weight of one stack section. Hence, the possibility of transfer of printed images from one sheet to another because of the weight of overlying sheets is minimized.

The vertical conveyors may move at either of two speeds. When sheets are being delivered to a particular stack receiving location, the conveyors are always moving slowly downward under the control of photoelectric cells, so that the downward speed of the conveyors equals the speed with which the stack is built up. When no sheets are being delivered, the conveyors may be moved rapidly under manual control, for convenience in unloading a stack and inserting an unloaded pallet at the bottom of the conveyor and driving it upwardly to bring the pallet to its highest elevation where it receives the fresh sheets from the conveyor. 7

At each stack receiving means, there is provided an array of vacuum wheels over which the sheets approaching the stack receiving means are drawn. The vacuum wheels pull the trailing edges of the printed sheets taut and keep them from dragging on the apparatus over which they are passing. The vacuum wheels are rotated so that their peripheral speed is less than the linear speed of the passing sheets. The wheels are thereby effective to pull the sheets away from the grippers. Thetwo arrays of vacuum wheels are provided with a common drive so that they rotate synchronously. The common drive includes a drive shaft with two universal joints at its opposite ends, to permit adjustment of the array of vacuum wheels longitudinally of the direction of movement of the delivery chain. A common adjusting mechanism is provided for changing the longitudinal positions of both sets of vacuum wheels. This common adjustment mechanism includes, for each set of vacuum wheels, a set of pinions running along racks on the opposite sides of the press and driven through a similar common drive shaft and universal joints, which may be manually operated. The vacuum wheels of each array are laterally adjustable on their supporting shaft. Biasing means are provided for the supporting shaft so as to take up any lost motion between the racks and pinions. The biasing means is in the form of flexible straps connected to the supporting shaft and extending over a horizontal shaft and thence downwardly to a weight. The biasing force is independent of the longitudinal adjustment of the vacuum wheel array and is also independent of the lateral adjustment of the vacuum wheels on the support shaft.

DRAWINGS FIG. I is an elevational view showing the delivery end of a printing press, and sheet delivery apparatus is accordance with the invention for delivering sheets from the press to two stack receiving positions.

FIG. 1A is a fragmentary view, similar to a portion of FIG. 1, illustrating a modification.

FIG. 2 is an elevational view taken from the rear of the sheet delivery apparatus as viewed in FIG. 1, on an enlarged scale, showing certain details of the stack receivers.

FIG. 3 is a fragmentary view, partly in section, taken along the line 33 of FIG. 2, on an enlarged scale, and with certain parts omitted.

FIG. 4 is a fragmentary sectional view taken along the line 44 of FIG. 3.

FIG. 5 is a sectional view taken along the line 5-5 of FIG. 2, on an enlarged scale, and also along the line 55 of FIG. 6, with certain parts broken away, and other omitted.

FIG. 6 is an elevational view taken along the line 66 of FIG. 5, with certain parts broken away.

FIG. 7 is a fragmentary sectional view taken along the line 77 of FIG. 6.

FIG. 8 is a fragmentary sectional view taken along the line 8-8 of FIG. 7, on an enlarged scale.

FIG. 9 is a fragmentary sectional view taken along the line 99 of FIG. 2, on an enlarged scale, and with certain parts omitted.

FIG. 10 is a fragmentary sectional view taken along the line 10-10 of FIG. 9, on an enlarged scale, with certain parts broken away and others omitted.

FIG. 11 is a fragmentary sectional view taken along the line 1Il1 of FIG. 9, on an enlarged scale, and with certain parts broken away.

FIG. 12 is a fragmentary sectional view taken along 6 the line 12--l2 of FIG. 10, with certain parts omitted.

FIG. 13 is a detailed view of stack 12 shown in FIG.

DETAILED DESCRIPTION FIG. 1

-This figure illustrates a printing press, generally indicated at 1, provided with a sheet delivery apparatus in accordance with the invention. The printing press includes a plate cylinder 2 and a pressure cylinder 3. Sheets to be printed are supplied to the pressure cylinder 3 from a sheet supply cylinder 4, and the printed sheets are removed from the pressure cylinder 3 by an endless delivery conveyor 5, usually a pair of laterally spaced chains 5a and 5b (FIGS. 3 and 4), running over sprocket wheels 6 at the press and over sprocket wheels 7 at the end of the conveyor remote from the press. The sheets move away from the press on the upper run of the conveyor 5 and are carried around the sprocket wheel 7 and thereafter pass two sheet stack receiving means 11 and 12, hereinafter sometimes referred to simply as stacks 11 and 12. Each of the stacking stations includes a base support 13 for a stack of sheets,

which may be a pallet, as shown, to facilitate removal of the stack of sheets by means of a fork lift truck. Each stack may include a plurality of separators, such as the stacking plates 14 of FIG. 1 or the pallets 8 of FIG. 1A, on each of which is supported a stack section 15.

After passing the stack receiving means 11 and 12, the chain 5 passes an inspection station 16, sometimes referred to as an auxiliary sheet receiving means, including a tray 17 which is movable between a normal sheet receiving position, shown in dotted lines in FIG. 1 and an inspection position shown in full lines. The tray 17 may be driven between its two positions by suitable motor means (not shown) controlled manually from a controller 18 located on the press frame under the tray. The tray 17 is latched in its sheet receiving position by a latch 20 releasable only from controller 18. This limited control of the latch 18 prevents accidental downward movement of the tray when a person is standing under it.

Each stacking station 11 and 12 also includes four vertical endless conveyors 21, one at each corner of the station. The conveyors 21, are typically chains and carry retractable brackets 19 which support the plates 14 during their downward travel, and which are pivoted so to retract upwardly (see FIG. 11) and pass by the ends of a plate 14, which has become stationary by virtue of reaching a resting position on one of the lower stack sections 15 or on the base support 13.

Instead of using the stacking plates 14, as shown in FIG. 1, the stack sections 15 may be received on a plurality of pallets 8, as shown in FIG. 1A. The pallets 8 are supported directly by the brackets 19. Note that the pallets 8 have legs which are longer than the height of the stack sections 15. Note also that the height of the legs plus the spacing thickness of the top of the pallets trated in FIG. 1B is suitable only where the characteristics of the paper and ink being used are such that a tall stack can be built up without encountering objectionable transfer of printing matter between adjacent sheets in the stack, when subjected to heavy pressure. Note that when the stack reaches its full height, and the pallet is resting on the floor, the lowermost sheets in the stack are subjected to the pressure from the entire stack of sheets. In the modification shown in FIGS. 1 and 1A, the maximum pressure to which any sheet is subjected during the building of the stack is the pressure due to the height of one stack section 15, rather than the pressure due to the height of the full stack.

In the modification of FIG. 1, the pallets 13 are narrower than the horizontal space between the brackets, and so rest upon the floor during the entire stacking operation. Alternatively, a wider pallet 8 or 10 could be used as in FIGS. 1A and 1B.

The pallets 8 of FIG. 1A and the plates 14 of FIG. 1 are inserted from the front or rear sides of the stack, at the top of the stack. They may be inserted by hand or by machine.

FIGS. 2 s

The delivery conveyor 5 includes a plurality of gripper means, each including an associated gripper release mechanism, shown in FIGS. 2-8.

As best seen in FIGS. 3 and 4, each gripper means includes a pair of plates 22, each fixed to one link of the chains 5a and 5b which make up the conveyor 5. Each plate 22 is aligned with another plate 22 on the opposite side of the press. Each pair of opposed plates 22 is connected by a fixed rod 24 attached at its ends to the plates 22 and by a gripper release shaft 25, which is rotatably mounted at its opposite ends in the plates 22.

Each of the fixed rods 24 carries a plurality of spaced gripper blocks 26 (see FIG. 8) which cooperate with an equal plurality of gripper fingers 27 carried by blocks 28 fixed on the rotatable shaft 25. At one end, the shaft 25 has fixed thereto an arm 31 having a cam follower roller 32 rotatably mounted at its outer end. As best seen in FIG. 4, the cam follower rollers 32 on one set of alternate gripper means are located on the left-hand sides of the arms 31, while the cam follower rollers 32 for the other set of alternate gripper means are located on the right-hand sides of the arms 31. Hence, one set of alternate cam followers 32 is spaced laterally of the conveyor 5 from the other set.

The shaft 25 has fixed thereto at spaced intervals, another set of crank arms 33 (FIGS. 4 and 8) which are apertured at their outer ends to-receive pivots 34 which are in turn apertured to receive one end of a rod 35. The opposite end of rod 35 has ahead 36 which is apertured to receive a pivot pin 38 fixed on a forked block 39 attached to the fixed rod 24. A spring 37 is retained in compression between the head 36 and a spring retaining washer 41 on the rod 35.

At times during the travel of the chain 5, the cam follower roller 32 engages a cam 42 and rotates the arm 31 counterclockwise, as viewed in FIGS. 6 and 8, thereby turning the shaft 25 counterclockwise and separating the gripper fingers 27 from the gripper block 26, so as to release the leading edge of a sheet 43 which has been retained between the finger 27 and the gripper block. After the cam follower 32 has passed on the cam 42, the springs 37 are effective to restore the arm 31 and the gripper fingers 27 to their normal gripping positions.

At each of the stack receiving means 11 and 12, there are two retractable cams, shown at 42 and 44 in FIG.

5, spaced laterally of the conveyor at locations corresponding to the positions of the two sets of cam followers 32, described above. The cam 42 is adjustably mounted by means of bolts 45 on a crank arm 46 having slots 46a to receive the bolts 45. The crank arm 46 is integral with a sleeve 46b rotatable on a stub shaft 47, which is fixed in a mounting plate 51 attached to a side frame member of the sheet delivery apparatus.

The sleeve 46b is keyed to a crank 48 having a forked crank arm 480 which receives at its end a pivot pin 54 to which one end of a piston rod 55 is pivotally connected. The piston rod 55 extends to a piston (not shown) in a'liydraulic cylinder 56 whose opposite end is pivoted on a pin 57 mounted on a bracket 58 attached to the mounting plate 51.

The other cam 44 is similarly mounted on a crank arm 53 by means of bolts 52, which extend through slots 53a. The crank arm 53 is integral with a sleeve 53b which is concentric with and rotatable on the outside of the sleeve 46b.

The sleeve 53b has an integral forked crank arm 53c supporting a crank pin 61 which serves as a pivot for one end of a piston rod 62 cooperating with a piston (not shown) in a hydraulic cylinder 63 which is also pivotally mounted at its opposite end on the pivot pin The sleeves 46b and 53b have integrally formed thereon projecting arms 46d and 53d which engage a stop pin 64 to limit the rotation of the sleeves in the counterclockwise direction as viewed in FIG. 6. The stop pin 64 is fixed in the mounting plate 51. The clockwise movement of the sleeves 46b and 53b is limited by another stop pin 65 which is in the path of movement of the upper sides of the earns 42 and 44.

The auxiliary sheet receiving means 16 is provided with a pair of selectively operable cams (not shown), similar to the cams 42 and 44, and similarly actuated, as explained below. It is alternatively possible to provide only one cam at each of the stack receiving means 11 and 12, but the auxiliary sheet receiving means 16 must have two.

The cams 42 and 44 control the release of the leading edges of sheets over the stack receiving means 11 and 12, as may be best seen in FIG. 2. The trailing edges of the sheets are supported as they approach the stack receiving means 11 and 12 by arrays of vacuum wheels 71, which appear in dotted lines in FIG. 2, and in full lines in FIGS. 9'-l2. The vacuum wheels 71 at each stack receiving station are keyed on a common shaft 72 which is journaled in a pair of upwardly extending projections 73 on a pair of housings 74 which may be moved longitudinally of the sheet delivery apparatus on a pair of rack rods 75. Each housing 74 slidably receives a rack rod 75 which has the rack teeth formed on its under side, as best seen in FIG. 12. Each pair of housings 74 also rotatably carries a shaft 76 which extends across the sheet delivery apparatus and has fixed thereon a pair of pinions 77 which cooperate with the racks 75.

The shafts 72 for both of the stack receiving means 11 and 12 are continuously rotated by a common drive shaft 81 through two sets of bevel gears 82. One of each set of bevel gears 82 is fixed on the common drive shaft 81 and the other is fixed on a stub shaft 83 (FIG. 12) whose opposite end is connected by a universal joint 84 to one end of a drive shaft 85. The other end of drive shaft 85 is connected through a universal joint 86 to an end of the vacuum wheel supporting shaft 72. The common drive shaft 81 is driven by a motor 87 (FIG. 2) through an appropriate shaft linkage including supported sections journaled in the frame of the sheet delivery apparatus and connected by universal joints to unsupported sections of the shaft to accommodate minor misalignments between the supported sections as may be required. The motor drives the vacuum wheels 71 at a peripheral speed slower than the speed of the passing sheets, so that the wheels 71 are effective to maintain the sheets under tension.

The pinion supporting shaft 76 of each of the stack receiving means 11 and 12 is driven from a common drive shaft 91 through a pair of bevel gears 92, a stub shaft 93, a universal joint 94, a drive shaft 95 and another universal joint 96 connected to the end of one of the shafts 76. The common drive shaft 91 for the two shafts 76 and their pinions 77 is rotatable by means of a hand wheel 97 (FIG. 2) provided with a locking wheel 98. The shaft 91 extends lengthwise of the sheet delivering mechanism, and includes supported sections and unsupported sections which are connected by universal joints between their ends and thesupported sections.

By loosening the lock wheel 98 and adjusting the hand wheel 97, the vacuum wheels 71 for both stack receiving means may be moved lengthwise of the sheet delivery apparatus as may be required to accommodate sheets of different widths received from the press. It is not expected that the range of adjustment required will be great, and should of course be within the capability of movement of the drive shaft linkages including the universal joints 84, 86, 94, 96.

The bolts 45, 52 and slots 46a, 53a allow adjustment of the cams 42 and 44 to provide a similar accommodation for sheets of different dynamic characteristics. In other words, some sheets present less air resistance than others, so that some sheets drop more quickly away from the conveyor when they are released. The sheets that drop more quickly must be carried along the conveyor a greater distance before they are released, if they are to drop in substantially the same stack location.

Between the two housings 74, on the opposite sides of the sheet delivery apparatus, there are provided two beams 121 and 122 (FIGS. and 12). The beam 121 adjustably supports a plurality of guides 123 which cooperate with the vacuum wheels 71 to keep the trailing edges of the sheets of paper from following too closely the periphery of the vacuum wheels, so that the sheets are separated completely from the vacuum wheels and fall onto the stacks without being delayed unduly by the presence of the vacuum wheels.

Adjacent each of the vacuum wheels 71, there is -fixed on the beam 122 a manifold 124 through which a source of vacuum (not shown) is connected to the peripheral ports 71a on the vacuum wheels. A flexible strap 125, preferably of metal, is attached to the top of each manifold 124 and extends over a rotatable transverse shaft 126 and thence downwardly. The lower end of the strap 125 carries a weight 127. The weights 127 are effective to bias the entire vacuum assembly, in-

Note that this bias is equally effective in all positions of the vacuum wheel assembly as it is adjusted longitudinally of the sheet delivery apparatus. It is also equally effective in any lateral adjustment of any of the vacuum wheels 71. In other words, the biasing force provided by this mechanism remains constant regardless of adjustments made in either the longitudinal position or the lateral positions of the vacuum wheels.

Each of the stack receiving means 11 and 12 comprises vertical conveyor means including four endless chains 101, each extending over an upper sprocket 102 and a lower sprocket 103. The lower sprocket 103 is provided with a conventional tension adjustment 104. Each chain 101 has fixed thereon at spaced intervals brackets 19, each bracket 19 comprising a link 105 (FIG. 11) supporting a pivoted arm 106. The arms 106 are biased by gravity so that as they move over the top sprocket 102 in the counter-clockwise direction as viewed in FIG. 11, they fall to horizontal positions. As viewed in FIG. 11, the bias acts counter-clockwise on the arms 106. Each arm 106 has a shoulder 106a which cooperates with a flange 105a on the link 105 to limit the rotation of the arm 106 in a clockwise direction. The brackets on the four chains 101 are at the same levels, and the four chains are maintained in synchronism since they are driven from a common drive motor 107 (FIG. 2). As each pair of brackets 106 starts to move downwardly, a plate 14 is inserted either manually or by a suitable apparatus (not shown), so as to be supported on an array of four brackets at the same level. Each stack section 15 builds up on the uppermost plate 14 being supported and guided and aligned thereon by a conventional jogger mechanism, shown only diagrammatically in FIG. 13 as a pair of vertical plates 108, which are horizontally reciprocated by means not shown. As the plates 14 and the stack sections 15 thereon move downwardly on the chains 101, the lowermost plate 14 eventually comes to rest on the pallet 13 and the plate 14 immediately above it later comes to rest on the lowermost stack section 15. The subsequent stack plates and stack sections all come to rest, one after the other, on the stack sections below them. The arrangement just described gives the sheets a substantial drying time for the ink to set before they are subjected to the pressure of more than the small number of sheets represented by a single stack section 15. The lowermost stack section does not begin to receive pressure from stack sections above it until it has reached the pallet 13 and is supported by the pallet.

After a particular plate 14 is supported either by the pallet 13 or by a stack section 15 immediately under it, then the brackets 19 move downwardly away from the plate which is so supported. The arms 106 are pivoted by engagement of the lower plates and pass by them without interference.

Instead of using gravity bias to hold the arms 106 in their projected positions, springs may be employed for this purpose. The particular biasing arrangement emcluding housings 74 and the parts associated therewith toward the shaft 126 and thereby to take up all lost motion in the driving connections for the shafts 72 and 76.

ployed does not affect the operation, as long as it permits the arms to move to their retracted positions to pass the stationary plates 14 without interference.

Each pair of front and rear sprockets 102 is fixed on a shaft 11 1, which extends from front to rear across the sheet delivery apparatus. The two shafts 111 for each stacking station are driven by a motor 107 (FIG. 2) through a reduction gear 112 and a suitable shaft 113. The lower sprockets 103 are similarly fixed on rotat- 

1. Sheet delivery apparatus for receiving sheets from a printing press and carrying the sheets selectively to either of two sheet receiving positions, comprising: a. two sheet receiving means, one at each of said positions; b. an endless delivery conveyor extending from between the printing press, past the two sheet receiving means in succession; c. means for driving the conveyor; d. a plurality of gripper means spaced along the conveyor, each gripper means being shiftable between a sheet gripping position and a sheet releasing position; e. a gripper release mechanism in each gripper means including a cam follower biased to a position in which the gripper means engages a sheet, and movable therefrom to a retracted, sheet releasing position;
 1. the cam followers for a first set of gripper means being spaced laterally of the direction of movement of the conveyor from the cam followers of a second set; f. two cams in each sheet receiving means, respectively aligned with the two sets of cam followers, for engaging the cam followers and thereby operating the gripper release mechanisms to their sheet releasing positions; and g. separate actuator means for each cam, each said actuator means being operable to move its associated cam between a retracted position in which the cam does not engage any of the cam followers, and an active position in which it engages the cam followers of one set of gripper means.
 2. Sheet delivery apparatus as in claim 1, in which the separate actuator means for the two cams in each sheet receiving means comprises: a. a shaft; b. a pair of concentric sleeves on said shaft; c. a pair of arms, each connected to one of said sleeves and each carrying one of said cams; and d. separate motor means for driving eaCh sleeve through a partial rotation on said shaft to drive the cam connected to said sleeve between said retracted position and said active position.
 2. a cross shaft at each stack receiving position carrying a row of said peripherally ported wheels; and
 2. a row of wheels extending across the path of movement of sheets on the conveyor, said wheels having peripheral ports movable tangentially to the sheets and connected to a source of vacuum and effective to restrain and control the movement of the trailing edges of the sheet;
 2. an endless delivery conveyor extending from between the printing press, past the two sheet receiving means in succession;
 2. a row of wheels extending across the path of movement of sheets on the conveyor, said wheels having peripheral ports movable tangentially to the sheets and connected to a source of vacuum and effective to restrain and control the movement of the trailing edges of the sheet;
 2. a longitudinally extending shaft carrying bevel gears cooperating with the bevel gears connected to the second cross shafts; and
 3. means for rotating said londitudinal shaft.
 3. stacker means for receiving and stacking sheets released by the gripper means, each said stacker means comprising: i. two horizontally spaced, downwardly traveling, opposed conveyor means; ii. retractable brackets on each said conveyor means projecting toward brackets on the opposite conveyor means; iii. common drive means for the two conveyor means; and iv. a plurality of separators, insertable in said stacker so as to be supported on a set of opposed brackets for receiving sheets; v. said brackets being retracted by engagement with any separator which has reached its limit of downward movement in an accumulating stack; f. common drive means for rotating the vacuum wheels at both of said receivers; and g. common means for adjusting longitudinally of the delivery conveyor the vacuum wheels at both said stack receiving means.
 3. means for driving the conveyor;
 3. Sheet delivery apparatus as in claim 2, in which said cams are adjustable on said arms.
 3. stacker means for receiving and stacking sheets released by the gripper means; f. common drive means for rotating the vacuum wheels at both of said receivers, including:
 3. drive means connecting both cross shafts to the longitudinal shaft, said drive means including, for each cross shaft: i. a drive shaft; ii. a pair of universal joints, one connected to each end of said drive shaft; iii. a set of bevel gears connecting said longitudinal shaft to one of said universal joints; iv. means connecting the other universal joint to the cross shaft; and
 4. means for rotating said longitudinal shaft; and g. common means for adjusting longitudinally of the delivery conveyor the vacuum wheels at both said stack receiving means.
 4. Sheet delivery apparatus as in claim 1, in which: a. each said sheet receiving means includes means for stacking a multiplicity of sheets; b. an auxiliary sheet receiving means of limited capacity as compared to the other two; c. two cams in the auxiliary sheet receiving means, respectively aligned with the two sets of cam followers; d. separate cam actuator means for the last-mentioned cams; and d. means for controlling the last-mentioned cam actuator means so as to maintain each cam in the auxiliary sheet receiving means in its retracted position unless all of the cams for the corresponding set of cam followers in the first two sheet receiving means are in their retracted positions.
 4. a plurality of gripper means spaced along the conveyor, each gripper means being shiftable between a sheet gripping position and a sheet releasing position;
 5. a gripper release mechanism in each gripper means including a cam follower biased to a position in which the gripper means engages a sheet, and movable therefrom to a retracted, sheet releasing posItion; i. the cam followers for a first set of gripper means being spaced laterally of the direction of movement of the conveyor from the cam followers of a second set; and
 5. Sheet delivery apparatus for receiving sheets from a printing press and carrying the sheets selectively to either of two sheets receiving positions, comprising: a. an endless delivery conveyor extending between the printing press and the stack receiving positions; b. means for driving the conveyor; c. a plurality of gripper means spaced along the conveyor, each gripper means being shiftable between a sheet gripping position and a sheet releasing position; d. a gripper release mechanism in each gripper means including a cam follower movable from a gripping position in which the gripper means engages a sheet to a sheet releasing position;
 6. two cams in each sheet receiving means, respectively aligned with the two sets of cam followers, for engaging the cam followers and thereby operating the gripper release mechanisms to their sheet releasing positions; and
 6. Sheet delivery apparatus as in claim 5, in which said common adjusting means includes: a. a pair of racks extending longitudinally on each side of the delivery conveyor; b. a second cross shaft at each stack receiving station; c. means on each second cross shaft supporting the corresponding first cross shaft; d. two pinions on each second cross shaft engaging said racks; and e. drive means for each cross shaft including:
 7. Sheet delivery apparatus as in claim 6, including: a. means for laterally adjusting the position of the peripherally ported wheels along the cross shaft; b. means biasing the cross shaft to maintain it at right angles with the longitudinal shaft and to take up lost motion in the rack and pinions.
 7. separate actuator means for each cam, each said actuator being operable to move its associated cam between a retracted position in which the cam does not engage any of the cam followers, and an active position in which it engages the cam followers of one set of gripper means.
 8. Sheet delivery apparatus as in claim 7, in which said biasing means comprises: a. a housing attached to each vacuum wheel and slidable on said cross shaft and non-rotatable with respect to the cross shaft; b. a transverse rod; c. a flexible strap attached at one end to the housing and extending over the transverse rod; d. a weight carried at the opposite end of said flexible strap and biasing said housing toward said transverse rod.
 9. Sheet delivery apparatus for receiving sheets from a printing press and carrying the sheets selectively to either of two sheet receiving positions, comprising: a. an endless delivery conveyor extending between the printing press and the stack receiving positions; b. means for driving the conveyor; c. a plurality of gripper means spaced along the conveyor, each gripper means being shiftable between a sheet gripping position and a sheet releasing position; d. a gripper release mechanism in each gripper means including a cam follower movable from a gripping position in which the gripper means engages a sheet to a sheet releasing position;
 10. Sheet delivery apparatus for receiving sheets from a printing press and carrying the sheets selectively to either of two principal receiving positions or to an auxiliary sheet receiving position, comprising: a. an endless delivery conveyor extending between the printing press and the stack receiving positions; b. means for driving the conveyor; c. a plurality of gripper means spaced along the conveyor, each gripper means being shiftable between a sheet gripping position and a sheet releasing position; d. two stack receiving means, one at each of said principal sheet receiving positions; e. stack Selector means operable to select delivery of all sheets to either one of said stacks or of alternate sheets to both of said stacks; f. sheet receiving means of limited capacity at said auxiliary stack receiving position; g. means for transferring to said auxiliary shehet receiving position all sheets which pass said principal stack receiving positions; h. time controlled means for operating said transferring means to disable the stack selector means for a predetermined time and during that time to deliver to the auxiliary sheet receiving means all sheets selected by the stack selector means for delivery to at least one stack; and i. means for selectively setting said time-controlled means to disable the stack selector means either for a first predetermined time of the order of the time required to deliver one sheet to the auxiliary receiving means, or for a second predetermined time of the order of one minute.
 11. Sheet delivery apparatus for receiving sheets from a printing press and carrying the sheets selectively to either of two principal receiving poistions or to an auxiliary sheet receiving position, comprising: a. an endless delivery conveyor extending between the printing press and the receiving positions; b. means for driving the conveyor; c. a plurality of gripper means spaced along the conveyor, each gripper means being shiftable between a sheet gripping position and a sheet releasing position; d. a gripper release mechanism in each gripper means including a cam follower movable from a gripping position in which the gripper means engages a sheet to a sheet releasing position, the cam followers for a first set of gripper means being spaced laterally of the direction of movement of the conveyor from the cam followers of a second set; e. two principal stack receiving means, one at each of said principal sheet receiving positions; f. auxiliary stack receiving means of limited capacity at said auxiliary stack receiving position; e. each of said receiving means including two cams respectively aligned with the two sets of cam followers for engaging the cam followers of said two sets of gripper means and operating the respective gripper release mechanisms to their sheet releasing positions; h. separate actuator means for each cam, each said actuator means being operable to move its associated cam between a retracted position in which the cam does not engage any of the cam followers, and an active position in which it engages the cam followers of one set of gripper means; and i. means responsive to the retraction of the cams for operating one set of gripper release mechanisms at both of said principal sheet receiving positions to operate the corresponding cam at the auxiliary sheet receiving position to its active position.
 12. Printing apparatus, comprising: a. a cylinder carrying two printing plates; b. a single feeder for feeding sheets to said cylinder so that successive sheets from the feeder are alternately printed by the two plates; and c. double stacking means for delivering sheets from the press alternately to two stacks, so that all of the sheets printed by one plate are delivered to one stack and all of the sheets printed by the other plate are delivered to the other stack, said double stacking means comprising; 